NATHAN BLENCHARCZYK, 28
JOE GEBBIA, 29
AND BRIAN CHESKY, 29
Founders, AIR BNB

Airbnb founders Brian Chesky and Joe Gebbia were just looking to make some quick cash when they turned their San Francisco apartment into an impromptu B&B for out-of-town conventioneers. But soon the two college friends, along with Nathan Blecharczyk, a former Microsoft employee, realized they were sitting on a legitimate business opportunity: a website that could pair savvy travelers with underutilized spaces. To help fund their start-up, they raised $30,000 by selling collectible breakfast cereals called Obama O's and Cap'n McCain's. Three years later, Airbnb has more than 100,000 listings—ranging from urban lofts to Yorkshire castles—in almost every country in the world, leading to new vacation experiences for travelers and new income streams for people with spare bedrooms. "We'll probably have more rooms than Hilton by next year," Chesky says.

VITAL SIGNS

Year Founded: 2008
Home Base: San Francisco
Number of Employees: 130
Number of Nights Booked: More than 2 million
Estimated Valuation: $1.3 billion

USER DATA

How Airbnb job training is different:
"The place where we started is really important to our history, so we bring every new employee to the apartment to give him an hour-and-a-half tour." — Chesky

The celebrities you'll find at HQ:
"We had an office-warming with, like, 500 people. Our DJ was none other than MC Hammer. He's a huge fan of Airbnb. We actually had a dance-off. It was a little bit surreal." — Gebbia

What it's like to get the celebrity treatment yourself:
"I have an extra bedroom that I rent out. I have a lot of young entrepreneurs from out of town stay with me. When they ask what do I do, I say I work for a start-up, and they say, 'What start-up?' I tell them Airbnb, and the reaction—it's pretty awesome." — Blecharczyk

Favorite Airbnb stay:
"I had this one, like, a block from Dolores Park in San Francisco. It was beautifully furnished, and you could step out of the apartment and feel like a local." — Chesky

Why we love what we do:
"We got an e-mail from a couple in New York City who lost their jobs. They decided, 'Well, why don't we just list our extra bedroom on Airbnb?' Their listing became so successful that they ended up being able to acquire the apartment across the hall and list that on the site as well. That story is not unique." — Gebbia


DENNIS CROWLEY, 34
Cofounder and CEO, Foursquare

You may think that collecting badges and striving to become the mayor of your local coffee shop is kids' stuff, but Foursquare's 10 million devoted users think otherwise. The service, which Dennis Crowley launched two years ago with partner Naveen Selvadurai, has brought social networking mobile by persuading people to tell friends where they're eating, shopping, and hanging out via GPS-equipped smartphones. "We're solving very hard technical problems," Crowley says, "but the hardest thing for me personally is to figure out how to keep the company running efficiently as we get more people, more offices, and different personalities." Then there's the challenge posed by giants like Google and Facebook, both of which are eager to co-opt the check-in trend Foursquare started. But Crowley is holding strong: He has more experience in this realm than just about anybody, having launched his first location-based app, Dodgeball, seven years before the first iPhone—while still a student at NYU.

VITAL SIGNS

Year founded: 2009
Home Base: New York City
Number of Employees: 75
Number of Users: 10 million
Estimated Valuation: $600 million

USER DATA

Where I don't check in:
"My mom told me not to check in at church anymore. That's a new rule since I dropped my phone at Christmas Mass."

How demanding my job is:
"After we did the Series B round of financing, I went to the World Cup with my brother. That was the first time I took time off since starting Foursquare."

Why I'm based in New York:
"Tech is not the thing that defines New York—there's also finance, publishing, media, fashion. Our beta testers worked in all different industries, and the product became more interesting."

How people are using Foursquare:
"In the early days, we saw people checking in 20 times a day and I'd be like, 'You're not supposed to do that.' Whatever—people will check in however they want. The average user checks in, like, three times a day. I'd say I'm about that."